They obtained their measure, know it as a reflection.

This couplet speaks about the undeniable truth of consequences. It suggests that whatever actions one performs, the results, or 'proofs,' will always manifest. Think of it like a shadow: just as your shadow always accompanies you and is a clear reflection of your presence, so too are the outcomes of your deeds always with you, evident and inescapable. It's a profound reminder that our actions have definite and observable repercussions, much like a shadow faithfully follows its source, making our deeds manifest and known.